1. Field
One embodiment of the present invention relates to a method of manufacturing a magnetic recording medium.
2. Description of the Related Art
In the information-oriented society in recent years, the amount of data that needs to be stored in a recording medium has been continually increasing. To keep up with the increase in amount of data, there has been a demand for a recording apparatus and a recording medium with a dramatically high recording density. As regards a hard disk for which there is an increasing demand as a high-capacity and inexpensive magnetic recording medium, it is predicted that a recording density of one terabits per square inch or more, which is about ten times higher than the current recording density, will be required several years after.
In an existing magnetic recording medium used in a hard disk, one bit is recorded in a specific region of a thin film made of polycrystals of fine magnetic grains. To improve the recording capacity of the magnetic recording medium, therefore, the recording density must be increased. For this purpose, it is effective to reduce a recording mark size usable in recording per bit. If, however, the recording mark size is simply reduced, effect of recording noise caused by the shape of fine magnetic grains cannot be neglected. Instead, if the fine magnetic grains are reduced in size, it is impossible to maintain the data recorded in fine magnetic grains at an ordinary temperature due to a problem of thermal fluctuation.
To avoid these problems, it is proposed to use a bit patterned medium in which dots of recording material are separated by a non-recording material in advance so as to perform read and write using a single recording dot as a single recording cell.
Also, the problem that interference between adjacent tracks makes it difficult to increase the track density becomes marked in a magnetic recording medium installed in an HDD. In particular, reducing write blurring of a write head magnetic field is a serious technical problem. To solve the problem, a discrete track patterned medium (DTR medium) is proposed in which recording tracks are separated by processing a magnetic recording layer. The DTR medium can increase the track density because it can reduce the side erase phenomenon that information on an adjacent track is erased in writing, and the side read phenomenon that information on an adjacent track is read out in reading. Accordingly, the DTR medium is expected as a magnetic recording medium capable of achieving a high recording density. It should be noted that when using the term “patterned medium” in a broad sense the term includes the bit patterned medium and DTR medium.
In manufacturing the patterned medium including the DTR medium, reducing the track pitch directly increases the tack density and recording density eventually. The track pitch finally depends on the width of the sidewall, i.e., tapered portion, of a magnetic pattern; the smaller the width of the sidewall, the smaller the track pitch. That is, the track density can be improved if it is possible to form magnetic patterns of a highly rectangular shape. Also, since the error rate is lowered as the magnetic spacing between the head and the magnetic recording layer is made smaller, the magnetic spacing is important.
In a conventional method of manufacturing a patterned medium, a resist is applied to a magnetic recording layer, patterns of protrusions and recesses are transferred from a stamper onto a resist by imprinting, and then the magnetic recording layer is etched using the resist patterns as masks to form magnetic patterns. Since difference between an etching rate of the resist and that of the magnetic recording layer made of metal is small, however, the thickness of the resist is made larger the required processing depth.
To solve the problem, a method is used in which a hard mask made of carbon (C) having a lower etching rate than that of the magnetic recording layer is used, patterns of protrusions and recesses of the resist are transferred to the hard mask, and the magnetic recording layer is etched using the hard mask patterns as masks. Use of the hard mask enables manufacturing of a patterned medium having magnetic patterns with a good rectangular shape.
In order to improve the recording density of the medium installed in a hard disk drive, it is necessary to reduce the effective magnetic spacing between the head and the medium. In order to reduce the magnetic spacing, it is necessary to strip off the hard mask completely. In view of reducing the process time for stripping off the hard mask, it is suitable to employ reactive ion etching (RIE), which can enhance the etching rate of carbon. Since oxygen is likely to react with the magnetic recording layer, however, the magnetic recording layer is oxidized in the step of stripping the hard mask, and there is a risk of deterioration the error rate.
Japanese Patent No. 3844755 describes a method comprising: forming a first mask layer made of TiN and a second mask layer made of Ni on a magnetic recording layer, applying a resist thereto, imprinting a stamper to the resist, and sequentially etching those layers to form magnetic patterns. In this method, however, it has been found that the sidewall of the magnetic pattern formed has a large width. Therefore, the method causes a problem that the resultant medium has poor resistance against recording to the neighboring track under a desired track density.